I find it very surprising that some people question the idea that it’s unhealthy to take in a lot of salt, seeing as this idea is supported by a wealth of scientific evidence, including evidence indicating that hominins evolved on a low-salt diet, as well as by well-established, proven biological and physiological principles, concepts, and theories, chief of which is arguably the most powerful scientific theory of all: Darwin’s theory of evolution via natural selection. Whole food diets are by default low in salt; hence, I find it very difficult to understand how we humans could possibly have evolved a need to take in a lot of salt on a daily basis.
Among nutritionists and nutritional scientists, it’s well known that high salt intakes are linked with hypertension and heart disease. The vast majority (not all) hold the belief that it’s unwise to consume a lot of salt. This shouldn’t immediately lead us to conclude that it is indeed unwise to take in a lot of salt, seeing as the fact that something is generally agreed upon doesn’t necessarily mean that it’s correct; however, it should cause us to think twice before we jump ship and start swimming towards one that holds more sodium – one of the principal components of common salt.
My personal thoughts on the salt issue
I don’t claim to be an expert on salt or know everything about how the consumption of salt affects our health. What I do know though, is that all nutritional concepts and ideas have to conform to basic rules of evolution and biology to be valid. In my mind, the idea that it’s unproblematic to add significant quantities of salt to one’s diet doesn’t live up to this criterion.
I don’t have a horse in the salt race. I don’t really care whether it’s unhealthy or not to add salt to one’s diet. All I care about is finding out what’s correct/true. If I were to be presented with strong evidence that contradicts my current opinions, I would certainly be open to changing my stance on salt. With that said, I find it very unlikely that I will change my tune on the salt issue, seeing as the idea that it’s unwise to take in a lot of salt is, as I see it, supported by a wealth of scientific evidence.
This doesn’t mean that we should avoid salt like the plague or that it’s very harmful to add a pinch of table salt to one’s dinner. In the big scheme of things, I don’t think the high salt content is the biggest problem with the modern, western diet. I find it more concerning that people are taking in so much sugar and refined fat. With that said, salt is not benign. I would argue that we would all be wise to think twice before we add significant quantities of table salt or salty foods to our diets.
10 scientific papers that highlight the detrimental health effects that go hand in hand with the consumption of high-salt diets
The process of conducting nutritional research is not straight-forward. Different studies have different designs and examine similar phenomenons from different angles. Moreover, scientists are just humans; they make mistakes, vary with respects to their competence level, and don’t know everything there is to know about the things they study. Hence, it’s not surprising that not all studies that examine similar hypotheses come to similar conclusions.
It’s certainly possible to find studies that appear to show that salt is, in the grand scheme of things, largely benign; however, these studies are few and far between when compared to those showing that salt is not benign. Moreover, if one carefully looks into their methodological design, limitations and weaknesses typically reveal themselves. As I see it, the weight of the evidence clearly shows that it’s unwise to consume a lot of salt.
Below are 10 papers that cover some of the massive amount of research linking high salt intakes with unfavorable health outcomes…
1. Salt and hypertension: why is there still a debate?
This paper, which was published in 2013, describes the relationship between salt and hypertension and highlights the fact that a solid body of evidence shows that it’s problematic to consume a lot of salt.
From the abstract:
More than a quarter of human populations now suffer from hypertension paralleling the marked increase in the dietary intake of salt during the recent several decades. Despite overwhelming experimental and epidemiological evidence, some still debate the relation between salt and hypertension. Pointing to some conflicting data in a few flawed studies, they argue that policy interventions to reduce the dietary intake of salt are premature and maybe unsafe without further studies. A brief review of data relating salt intake to hypertension, along with an overview of the history of the introduction of salt to human diet on an historic and evolutionary time scale, should help dispel doubts on the effectiveness and safety of low-salt diet. The recorded history confirms how rare and inaccessible salt has been until recent times. Like all other terrestrial life forms, humans evolved in a salt-free environment under intense evolutionary pressure for the selection of salt-conserving genes. Hypertension is a prototypical evolutionary maladaptation disorder of the modern man—a species exquisitely well adapted to low salt conditions suddenly confronted with salt excess. The World Health Organization and many governments have finally taken action to reduce dietary intake of salt, which already has started to reduce the burden of hypertension and the associated cardiovascular morbidity and mortality. This brief review is to broadly look at the evidence linking salt to hypertension from a historic and evolutionary perspective as well as touching upon some of the epidemiological and experimental data.
2. Book chapter: Human Diet Before Modern Times
This is not a scientific paper per se, but rather a science-based chapter from an unpublished book entitled Sodium: “NO!” Potassium: “Yes!”, which was written by Birger Jansson (PhD), an expert on salt and the health effects of salt consumption. Dr. Jansson unfortunately died shortly after completing his book and therefore never got around to publishing it. Chapter 2 of the book, which was made available online by Dr. Loren Cordain quite recently, explains how humans’ intake of salt has changed throughout time. Perhaps needless to say, this chapter is very relevant with respects to determining our salt requirements.
In the concluding remarks of the chapter, Jansson has the following to say:
We conclude that primitive people have a very low intake of sodium. It may be of the order of 1-2 g per day or less. Their potassium intake is high and their dietary potassium to sodium ratio is over 10 and can be up to 100 or more. When agriculture necessitated food preservation the sodium intake increased in some instances to 100 g or more per day. This change in the intake of a nutrient, that in small quantities is essential but in great quantities toxic, is one of the greatest changes in the human diet that has ever occurred in the short time period of only a few thousand years. The slow human evolution has not had time to adapt our species to this change. Consequently, our intake of sodium has been and still is un-physiologically high while at the same time our intake of potassium is too low. This has caused an increase in a number of so-called diseases of civilization and among them cancer.
3. Effects of salt substitutes on blood pressure: a meta-analysis of randomized controlled trials
The meta-analysis of randomized controlled trials, published in 2014 in the American Journal of Clinical Nutrition, found that salt-substitution strategies are effective at lowering systolic and diastolic blood pressure.
In their concluding remarks, the authors has the following to say.
In conclusion, results of our meta-analysis suggest that salt substitutes are effective at lowering SBP and DBP. Salt substitution may therefore be a viable dietary approach for population-level hypertension control. Given that high BP was recently ranked the number one risk factor for the global burden of disease (46), identifying culturally appropriate, economically sustainable interventions with long-term effectiveness is of utmost importance. Salt substitution shows promise, but more studies in large diverse samples are needed to demonstrate their utility at the population level.
4. Effect of longer term modest salt reduction on blood pressure: Cochrane systematic review and meta-analysis of randomised trials.
This systematic review and meta-analysis, published by Cochrane in 2013, pooled the results of 34 randomized trials on the effects of long-term modest salt reduction on blood pressure.
It found the following (from the conclusion):
A modest reduction in salt intake for four or more weeks causes significant and, from a population viewpoint, important falls in blood pressure in both hypertensive and normotensive individuals, irrespective of sex and ethnic group. Salt reduction is associated with a small physiological increase in plasma renin activity, aldosterone, and noradrenaline and no significant change in lipid concentrations. These results support a reduction in population salt intake, which will lower population blood pressure and thereby reduce cardiovascular disease. The observed significant association between the reduction in 24 hour urinary sodium and the fall in systolic blood pressure, indicates that larger reductions in salt intake will lead to larger falls in systolic blood pressure. The current recommendations to reduce salt intake from 9-12 to 5-6 g/day will have a major effect on blood pressure, but a further reduction to 3 g/day will have a greater effect and should become the long term target for population salt intake.
5. Links Between Dietary Salt Intake, Renal Salt Handling, Blood Pressure, and Cardiovascular Diseases
This paper, which was published in 2005, includes a comprehensive discussion of how salt affects our health, as well as the amount of salt that humans have been consuming throughout history.
Epidemiological, migration, intervention, and genetic studies in humans and animals provide very strong evidence of a causal link between high salt intake and high blood pressure. The mechanisms by which dietary salt increases arterial pressure are not fully understood, but they seem related to the inability of the kidneys to excrete large amounts of salt. From an evolutionary viewpoint, the human species is adapted to ingest and excrete <1 g of salt per day, at least 10 times less than the average values currently observed in industrialized and urbanized countries. Independent of the rise in blood pressure, dietary salt also increases cardiac left ventricular mass, arterial thickness and stiffness, the incidence of strokes, and the severity of cardiac failure. Thus chronic exposure to a high-salt diet appears to be a major factor involved in the frequent occurrence of hypertension and cardiovascular diseases in human populations.
6. An Evolutionary Perspective of Nutrition and Inflammation as Mechanisms of Cardiovascular Disease
This paper, published in 2015, looks into the evolutionary origins of cardiovascular disease.
The following paragraph explains why we humans don’t do well on high-salt diets.
For millions of years, the ancestors of humans were adapted to an environment free of salt, with an elevated evolutionary pressure for the selection of salt conserving genes such as the angiotensinogen gene  and the ACE gene . Therefore, hypertension also has an evolutionary origin based on salt intake. There are variants of salt conserving enzymes whose activity is associated with an increase in water and sodium retention. These variants may have had some advantages for humans to adapt to the ancestral environment before the human race expanded to Asia and Europe. However, when humans inhabited regions where the climate became colder or wetter, salt and water retention became harmful. The presence of these genes increased susceptibility to hypertension . The change of salt ingestion of the human species has represented an evolutionary mismatch with terrible health consequences . Excessive salt increases water retention by peripheral tissues and in the kidney, increasing blood pressure.
7. Evolution of blood pressure regulation in humans.
This paper, which focuses on the evolution of blood pressure regulation in humans, had the following to say about the health effects of salt consumption (from the abstract):
The human propensity for hypertension is a product, in part, of our evolutionary history. Adaptation to climate, first in Africa and then throughout the world, has driven our evolution and may have shaped current patterns of hypertension susceptibility. This article reviews human evolution and the impact of climatic adaptation on blood pressure physiology. Evidence suggests that genetic susceptibility to hypertension is ancestral and was magnified during early human evolution. Furthermore, differential susceptibility among human populations is due to differential selection during the out-of-Africa expansion 30,000 to 100,000 years ago. The most important selection pressure was climate, which produced a latitudinal cline in hypertension susceptibility. Therefore, the current epidemic of hypertension is likely due to new exposures of the modern period (e.g.: higher salt intake) interacting with ancestral susceptibility. Worldwide populations may differ in susceptibility to the new exposures, however, such that those from hot, arid environments are more susceptible to hypertension than populations from cold environments.
8. Cardiovascular and other effects of salt consumption
Much of the research on salt has focused on the cardiovascular impacts of salt consumption. The author of this scientific paper, which was published in 2013, argues that more attention should be devoted to how salt affects other facets of our physiology.
He had the following to say in his concluding remarks:
The case for a reduction in salt intake for the prevention of cardiovascular disease is overwhelming. The present short review highlights many additional health benefits, some with more direct evidence and some still providing circumstantial support . The latter provide clear indication for research gaps to be followed to extend our knowledge of the benefit of a moderate reduction in salt intake.
9. Importance of salt in determining blood pressure in children: meta-analysis of controlled trials.
Most of the research on the health effects of salt consumption has focused on adult populations. This meta-analysis is different, in that its research data are derived from studies on children.
From the abstract:
This is the first meta-analysis of salt reduction in children, and it demonstrates that a modest reduction in salt intake causes immediate falls in blood pressure and, if continued, may well lessen the subsequent rise in blood pressure with age. This would result in major reductions in cardiovascular disease. These results in conjunction with other evidence provide strong support for a reduction in salt intake in children.
10. Salt intake, stroke, and cardiovascular disease: meta-analysis of prospective studies
This meta-analysis of prospective studies, published in 2014, found the following:
High salt intake is associated with significantly increased risk of stroke and total cardiovascular disease. Because of imprecision in measurement of salt intake, these effect sizes are likely to be underestimated. These results support the role of a substantial population reduction in salt intake for the prevention of cardiovascular disease.